Turbocharged and supercharged engines may be configured to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, an intercooler or charge air cooler (CAC) may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. Condensate may collect at the bottom of the CAC, or in the internal passages, and cooling turbulators. Under certain air flow conditions, condensate may exit the CAC and enter an intake manifold of the engine as water droplets. If too much condensate is ingested by the engine, engine misfire and/or combustion instability may occur.
Other attempts to address engine misfire due to condensate ingestion include avoiding condensate build-up. In one example, the cooling efficiency of the CAC may be decreased in order to reduce condensate formation. However, the inventors herein have recognized potential issues with such methods. Specifically, while some methods may reduce or slow condensate formation in the CAC, condensate may still build up over time. If this build-up cannot be stopped, ingestion of the condensate during acceleration may cause engine misfire. Additionally, in another example, engine actuators may be adjusted to increase combustion stability during condensate ingestion. In one example, the condensate ingestion may be based on a mass air flow rate and amount of condensate in the CAC; however, these parameters may not accurately reflect the amount of water in the charge air exiting the CAC and entering the intake manifold. As a result, engine misfire and/or unstable combustion may still occur.
In one example, the issues described above may be addressed by a method for adjusting engine operation and generating diagnostics responsive to water storage parameters at a charge air cooler (CAC), the water storage parameters based on an output of a first oxygen sensor positioned downstream of the charge air cooler and an output of a second oxygen sensor positioned upstream of the charge air cooler. Specifically, the first oxygen sensor may be positioned at an outlet of the CAC and the second oxygen sensor may be positioned at an inlet of the CAC. The oxygen sensors may be modulated between a variable voltage mode and a base mode at a rate based on exhaust gas recirculation (EGR) flow. For example, if EGR flow is greater than a threshold, the oxygen sensors may operate in the variable voltage mode for a shorter amount of time (e.g., modulate more frequently) in order to measure oxygen content of the charge air at the inlet and outlet of the CAC. An engine controller may use the outputs of the first oxygen sensor and the second oxygen sensor to determine water storage parameters at the CAC. In one example, the water storage parameters may include one or more of a water release amount from the CAC, a water release rate from the CAC, a water storage amount in the CAC, and a water storage rate in the CAC. The engine controller may then adjust engine operation to increase combustion stability, decrease condensate formation in the CAC, and/or evacuate condensate from the CAC in response to the determined water storage parameters. As a result, engine misfire and combustion instability due to water ingestion may be decreased.
In another example, degradation of the first oxygen sensor and the second oxygen sensor may be indicated based on engine operating conditions. Specifically, during engine operation when condensate less than a threshold is forming in the CAC and condensate less than a threshold is leaving the CAC, the engine controller may indicate degradation of the first oxygen sensor and the second oxygen sensor based on outputs of the first and second oxygen sensor relative to one another. Engine operation with condensate less than a threshold (e.g., substantially no condensate) forming in and leaving the CAC may be identified based on alternative condensate models and/or engine operating conditions. During this engine operation, when the output of the first oxygen sensor is not within a threshold of the output of the second oxygen sensor, the controller may indicate degradation of one or more of the first oxygen sensor and the second oxygen sensor. In this way, function of the oxygen sensors may be diagnosed, thereby increasing accuracy of the water storage parameter estimates.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.